A Study of the Salt-Water Intrusion Problem Between Salina, Kansas, and Solomon, Kansas, in the Smoky Hill River Valley

Abstract

Between Salina and Enterprise, Kansas, the Smoky Hill River picks up a considerable amount of saline water. The result is that the river downstream during low flows may exceed the recommended drinking-water quality standards for chloride. The Smoky Hill and Kansas rivers are important sources of water for several population centers in eastern Kansas. Therefore, this problem has a considerable impact on a significant part of the Kansas population.

The source of the saline water is predominantly from groundwater dissolution of the Hutchinson Salt Member of the Wellington Formation of Permian Age, with smaller amounts coming from disposal of oil field brines. The dissolution of the salt has caused a collapsed zone to occur trending north-south along the present eastern extent of the salt. This collapsed zone forms a briney aquifer called the Wellington aquifer. The brine in the Wellington aquifer flows generally eastward beneath the Smoky Hill Valley and contaminates the alluvial aquifer and river system primarily between New Cambria and Solomon, Kansas.

Considerable geohydrologic information is available about the problem area, although much more is needed before we can put together a detailed picture of the salt-water intrusion problem. The purpose of this project is to gain a better understanding of the intrusion mechanisms and to evaluate the intrusion. Numerical and analytical models will be applied to the system. These models will be applied within the framework of existing data.

In summary, the groundwater modeling of the Wellington aquifer has shown that:

The optimum (maximum salt-water reduction with fewest wells) well field configuration of all that we tested is a line of six relief wells spaced 2,000 feet apart, oriented north-south near the existing cottonwood tree well, each well discharging 100 gpm of brine from the Wellington aquifer.

The well configuration described in 1) will produce a 12-20% reduction of salt-water leakage from the Wellington aquifer with about a 245-382% increase in fresh-water leakage from the alluvial aquifer into the Wellington aquifer.

Some aspects of the model results were fairly sensitive to the input parameters and some effort should be expended to obtain better information before a more detailed model study is instigated or before relief well construction begins. However, the results presented in this study are not expected to be significantly changed. In particular, the percent reduction of salt-water leakage is not as strongly dependent on the model as one might expect. It is not likely that any Wellington aquifer relief well scheme could achieve a 50% volume reduction in salt-water discharge, if the hydraulic conductivity determined by the USGS on a shale core is representative.

The steady-state alluvial models presented in this investigation indicate that the salt water in the Smoky Hill River Valley should be in an unstable condition near the river. This indicates that unstable upconing should be a dominant mechanism for feeding salt water to the river system. The groundwater system does not uniformly discharge to the river system. The unstable upconing should be most pronounced in those reaches where the groundwater system consistently feeds the river system. These areas could be delineated by seepage and salinity surveys.

The time-varying alluvial model shows that the response of the chloride discharge to a flood event can be qualitatively explained by the unstable upconing mechanism. In addition, the time-varying model shows that several years would elapse before significant benefit would be seen in the river system from a Wellington aquifer relief well scheme.

The complete text of this report is available as an Adobe Acrobat PDF file.